Swiss Patent Application No. CH-A-636,323, published May 31, 1983, discloses a process in which the peripheral speed of an element which rotates synchronously with the running yarn speed is calculated using a pulse generating encoder. When the yarn speed is calculated in this way, an average value is attained, which is not always adequate in practice, since short fluctuations in the instantaneous speed cause inaccuracies when calculating certain yarn parameters.
When the yarn is wound on a very conical yarn package such as a cheese bobbin the winding diameter can differ by more than 200% between the small and large ends of the package. This results in instantaneous variations in the yarn speed, which are approximately equal, depending on whether the yarn is wound onto the small or large end portion of the package diameter. Such variations can render a spectrogram calculation unusable if immediately applied to spooling frames, or they can also cause considerable inaccuracies when calculating yarn parameters such as the lengths of slubs and neps.